Phase velocity of an electron with kinetic energy of 5eV and 50keV

1. Homework Statement
Consider electrons of kinetic energy 5eV and 500keV. For each electron, what would be the
particle speed, phase velocity, group velocity, and Broglie wavelength?

2. Homework Equations
lambda = h/p (lambda = broglie wavelength)
K.E. for nonrelativistic calcualtion = p^2/(2m)
phase velocity = lambda*f = lambda / time
group velocity = dw/dk

3. The Attempt at a Solution
So for the 5eV case, I found that since the energy is low, i can use non-relativistic calculation. I find the Broglie wavelength to be around 0.548 nm and the momentum to be 1.208E-24 kg(m/s). Knowing the momentum, I used p=mv to find the particle velocity, which came out to be around 1.326E6 m/s.

So far I think I am doing it right, but I cannot find the phase velocity nor the group velocity. Something tells me that for a non-relativistic case, the phase velocity is equal to c and the group velocity is equal to the particle speed. Can anyone explain this to me?

Also, how should I approach the 50keV electron case, since the energy is so high I need to use relativity.

Thanks.